The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Referring now to FIGS. 1A-1B, a Colpitts oscillator (hereinafter oscillator) 10 is shown. In FIG. 1A, the oscillator 10 comprises transistors T1 and T2 and a LC tank circuit 12. The LC tank circuit 12 includes inductances L, capacitances C1 and C2, and variable capacitances (varactors) Cv that may be included for tuning. A bias generator 20 generates biasing signals that bias the transistors T1 and T2 and the LC tank circuit 12. A frequency of an oscillator signal generated by the oscillator 10 is given by the following equation:
  f  =            1      /      2        ⁢    π    ⁢                  L        *                              C            ⁢                                                  ⁢            1            ⁢            C            ⁢                                                  ⁢            2                                              C              ⁢                                                          ⁢              1                        +                          C              ⁢                                                          ⁢              2                                          
The transistors T1 and T2 may include metal oxide semiconductor (MOS) transistors or bipolar junction transistors (BJTs). Flicker noise (also called phase noise) generated by the transistors T1 and T2 may be present in the oscillator signal. In FIG. 1B, a transistor (which can include transistors T1 or T2) is shown to comprise a source of flicker noise Vn1 in series with gate G of ideal transistor Q.
The frequency and/or amplitude of the flicker noise Vn1 may be less than the frequency and/or amplitude of the oscillator signal, respectively. The amount of flicker noise present in the oscillator signal may depend on the type of transistors used to implement the oscillator 10. For example, MOS transistors may generate a larger flicker noise than BJTs.